Embodiments relate to a light emitting device, a light emitting device package, and a lighting system.
In light emitting devices, P-N junction diodes having the properties of converting electrical energy into light energy may be formed by combining group III and V elements on the periodic table. Light emitting devices may implement various colors by controlling the composition ratio of compound semiconductors.
To form a white light emitting device package, light emitting devices of red, green and blue, which are the three primary colors of light, may be combined, or a yellow phosphor such as yttrium aluminum garnet (YAG) and terbium aluminum garnet (TAG) as a phosphor may be added to a blue light emitting device, or a (red/green/blue) three-colored phosphor as a phosphor may be added to a UV light emitting device.
A white light emitting device package including a phosphor may include a light emitting device on the bottom surface of a reflective cup of the package, and the reflective cup may be filled with an encapsulating material mixed with the phosphor. In this case, light having a first wavelength, which is emitted from the light emitting device may be mixed with light having a larger wavelength than the first wavelength, which collides with the phosphor, so as to form white light.
However, since the phosphor is mixed with encapsulating material to fill the reflective cup, it is necessary to provide the reflective cup to the package.
In addition, as the light emitting device comes closer to a phosphor layer, heat generated from the light emitting device is transferred to the phosphor layer to degrade wavelength conversion efficiency of the phosphor layer.
In addition, since phosphor particles sink during a process, concentration of phosphor may vary according to a process time.
In addition, color temperature deviation occurs according to a viewing angle.
In addition, since a yellow phosphor is applied on the outermost part of a blue LED, and light converted in the phosphor is naturally emitted, the light is emitted in all directions. At this point, light re-incident to a light emitting device is absorbed in the light emitting device to cause optical loss, thereby degrading light emitting efficiency.